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Abstract:

In a micronanobubble reaction vessel 3 of wastewater treatment equipment,
wastewater containing organic matter is treated with micronanobubbles.
Thereafter, the 5 wastewater is introduced into an aeration tank 7. Part
of organic matter in the wastewater is oxidized in the micronanobubble
reaction vessel 3 by micronanobubble treatment prior to treatment with
activity of microorganisms enhanced in the aeration tank 7. After organic
matter load is thus reduced, the treatment water is introduced into the
aeration tank 7, in which microorganisms exist in high concentration due
to submerged membranes 17, so that the organic matter in wastewater can
be effectively treated. This makes it possible to accomplish
miniaturization of the aeration tank 7, reduction in scale of the whole
equipment and therefore reduction in initial cost. Also, a photocatalyst
tank 22 is provided downstream of the aeration tank 7, so that a minute
amount of organic matter unaffected by the microbial treatment alone can
be oxidized at high-level by using a photocatalyst plate 24.

Claims:

1. A wastewater treatment method, comprising:a micronanobubble treatment
step for treating wastewater containing organic matter with
micronanobubble;a microbial treatment step for applying microbial
treatment with use of a submerged membrane to treatment water obtained by
treating the wastewater containing organic matter in the micronanobubble
treatment step; anda photocalytic step for applying photocalytic
treatment to treatment water after the microbial treatment step.

2. Wastewater treatment equipment, comprising:a micronanobubble reaction
vessel for receiving wastewater containing organic matter and treating
the wastewater containing organic matter with micronanobubbles;an
aeration tank for receiving treatment water from the micronanobubble
reaction vessel and applying microbial treatment to the treatment water
with a submerged membrane included in the aeration tank; anda
photocatalyst tank for receiving treatment water from the aeration tank
and applying photocalytic treatment to the treatment water.

4. The wastewater treatment equipment according to claim 2,wherein the
micronanobubble reaction vessel has: a micronanobubble generator; anda
water conveyance section for conveying treatment water from the aeration
tank to the micronanobubble generator through the submerged membrane.

5. The wastewater treatment equipment according to claim 2,wherein the
aeration tank has a micronanobubble cleaning section for generating
micronanobubbles to clean the submerged membrane.

6. The wastewater treatment equipment according to claim 5,wherein the
aeration tank has an air diffusion pipe for discharging air to the
submerged membrane to clean the submerged membrane, andthe submerged
membrane is cleaned with mixed bubbles composed of micronanobubbles
generated by the micronanobubble cleaning section and air discharged from
the air diffusion pipe.

7. The wastewater treatment equipment according to claim 6,wherein the air
diffusion pipe is placed below the submerged membrane while the
micronanobubble cleaning section is placed between the submerged membrane
and the air diffusion pipe, andwherein there are provided: a first guide
mounted on the air diffusion pipe for guiding air discharged from the air
diffusion pipe to the micronanobubble cleaning section; anda second guide
mounted on the submerged membrane for guiding micronanobubbles generated
by the micronanobubble cleaning section and air discharged from the air
diffusion pipe to the submerged membrane.

8. The wastewater treatment equipment according to claim 2,wherein the
aeration tank has a plurality of submerged membranes placed vertically in
two or more rows.

9. The wastewater treatment equipment according to claim 2,wherein the
photocatalyst tank has:an ultraviolet irradiation section; anda
photocatalyst plate which comes into contact with the treatment water and
which includes a sputtered thin film irradiated with ultraviolet light
from the ultraviolet irradiation section.

10. The wastewater treatment equipment according to claim 2,wherein the
photocatalyst tank has:a light emitting diode lamp; anda photocatalyst
plate which comes into contact with the treatment water and which
includes a sputtered thin film irradiated with light from the light
emitting diode lamp.

11. The wastewater treatment equipment according to claim 9,wherein the
photocatalyst plate includes the sputtered thin film and a substrate
which is made of either glass or quart.

12. The wastewater treatment equipment according to claim 10,wherein the
photocatalyst plate includes the sputtered thin film and a substrate,
andthe substrate is made of either glass or quart.

13. The wastewater treatment equipment according to claim 2,wherein the
photocatalyst tank has a micronanobubble generator.

14. The wastewater treatment equipment according to claim 2,wherein the
aeration tank receives treatment water subjected to biological treatment
or sludge generated after biological treatment.

15. The wastewater treatment equipment according to claim 9,wherein the
photocatalyst tank is structured to have a transparent outer wall, and
the ultraviolet irradiation section is placed around the transparent
outer wall.

16. The wastewater treatment equipment according to claim 10,wherein the
photocatalyst tank is structured to have a transparent outer wall, and an
ultraviolet irradiation section is placed around the transparent outer
wall.

[0002]Conventionally, general microbial treatment systems have an aeration
tank with a large capacity, which makes it difficult for factories having
smaller installation areas to install the aeration tank. This gives rise
to a demand for wastewater treatment methods and wastewater treatment
equipment which has a small installation area therefor as well as good
performance.

[0003]The high-concentration microbial treatment system with use of a
submerged membrane suffers a problem of reduction in filtered water
amount due to clogging of the submerged membrane as time Passes. This
gives rise to a demand for a method which makes it possible to
effectively clean oil and fat content on the surface of the submerged
membrane that causes clogging, even when the clogging of the submerged
membrane occurs.

[0004]In the case of systems involving only the high-concentration
microbial treatment, or in the case of requiring further advanced
treatment, treatment of activated carbon adsorption is sometimes added.
This causes a problem of higher running cost due to replacement of
activated carbon after adsorption of organic matter or the like. This
gives rise to a demand for a method which can effectively be cleaned oil
and fat content on the surface of the submerged membrane that causes
clogging, even when the clogging of the submerged membrane occurs.

[0005]As another prior art, JP2004-121962A has disclosed a treatment
method and a treatment device with use of nanobubbles.

[0006]This prior art utilizes characteristics of nanobubbles such as
decrease in buoyancy, increase in surface area, increase in surface
activity, generation of local high pressure fields, a surface active
property and an antiseptic property which are attained by achievement of
electrostatic polarization. More specifically, this prior art has
disclosed that the correlation among these characteristics shows a
fouling component adsorption function, a substance surface high-speed
cleaning function and an antiseptic function, so that it becomes possible
to clean various substances with high performance and low environmental
load so as to purify contaminated water.

[0008]In the nanobubble generation method according to this prior art,
there is provided with (1) a step for gasifying part of liquid by
decomposition in liquids, (2) a step for applying ultrasonic waves in
liquids, or (3) a step for gasifying part of liquid by decomposition and
a step for applying ultrasonic waves.

[0009]Both these two prior arts have disclosed purification of
contaminated water by using nanobubbles or removal of dirt on the surface
of solids by using nanobubbles. However, the two prior arts fail to
disclose any technology for enhancing efficiency in treatment and quality
of treated water by increasing the activity of microorganisms when
treating wastewater containing organic matter with use of microorganisms.

DISCLOSURE OF INVENTION

Subjects Which the Invention is To Solve

[0010]It is a primary object of the present invention to provide
wastewater treatment method and wastewater treatment equipment allowing
increase in treatment efficiency of wastewater containing organic matter
while achieving downsizing and reduction in running cost.

Means for Solving the Subjects

[0011]In order to achieve the above object, the present invention provide
a wastewater treatment method, comprising:

[0013]a microbial treatment step for applying microbial treatment with use
of a submerged membrane to treatment water obtained by treating the
wastewater containing organic matter in the micronanobubble treatment
step; and

[0014]a photocalytic step for applying photocalytic treatment to treatment
water after the microbial treatment step.

[0015]In the wastewater treatment method of the present invention, the
treatment water containing organic matter is subjected to pretreatment
with micronanobubbles in the micronanobubble treatment step. Then, the
treatment water is subjected to microbial treatment in the microbial
treatment step. Consequently, the effects of the pretreatment with the
micronanobubbles make it possible to reduce organic load or to increase
activity of microorganisms in the subsequent microbial treatment as well
as to downsize the equipment for microbial treatment.

[0016]Further, applying photocalytic treatment to the treatment water
after subjected to the microbial treatment in the microbial treatment
step allows photocalytic treatment of a minute amount of residual organic
matter contained in the treatment water, so that advanced treatment
beyond the limit of the treatment by the microbial treatment can be
achieved.

[0019]an aeration tank for receiving treatment water from the
micronanobubble reaction vessel and applying microbial treatment to the
treatment water with a submerged membrane included in the aeration tank;
and

[0020]a photocatalyst tank for receiving treatment water from the aeration
tank and applying photocalytic treatment to the treatment water.

[0021]In the wastewater treatment equipment of this embodiment, the
wastewater containing organic matter is treated with use of
micronanobubble in the micronanobubble reaction vessel, and thereafter
introduced into the aeration tank having a submerged membrane. In this
embodiment, therefore, prior to the microbial treatment in the aeration
tank, the wastewater containing organic matter is treated with
micronanobubbles in the micronanobubble reaction vessel. Consequently,
the organic matter in wastewater is oxidized by micronanobubbles to
reduce organic matter load, and thereafter the treatment water is
introduced into the aeration tank in which microorganisms are present in
high concentration by means of the submerged membrane, so that treatment
of organic matter is effectively accomplished. This allows
miniaturization of the aeration tank, reduction in scale of the whole
equipment and reduction in initial cost. In photocatalyst tank provided
downstream of the aeration tank, oxidation treatment using photocatalyst
makes it possible to perform high-level oxidation of a minute amount of
organic matter which has been unaffected by general microbial treatment
alone.

[0022]In one embodiment of the invention, the wastewater treatment
equipment further comprises

[0025]In the wastewater treatment equipment of this embodiment, the
micronanobubble reaction vessel receives wastewater containing organic
matter with quality and quantity adjusted in the adjustment tank, which
allows efficient oxidation of the organic matter by micronanobubble.

[0026]In one embodiment of the invention, the micronanobubble reaction
vessel has a micronanobubble generator, and

[0027]a water conveyance section for conveying treatment water from the
aeration tank to the micronanobubble generator through the submerged
membrane.

[0028]In the wastewater treatment equipment of this embodiment, the water
conveyance section conveys treatment water from the aeration tank to the
micronanobubble generator included in the micronanobubble reaction vessel
through the submerged membrane. In other words, the treatment water
(water containing electrolyte) is conveyed to the micronanobubble
generator from the aeration tank in which becomes the concentration of
microorganisms becomes high by means of the submerged membrane.
Consequently, the micronanobubble generator can stably supply extremely
fine bubbles in the micronanobubble reaction vessel.

[0029]In one embodiment of the invention, the aeration tank has a
micronanobubble cleaning section for generating micronanobubbles to clean
the submerged membrane.

[0030]In the wastewater treatment equipment, the micronanobubble cleaning
section can clean the submerged membrane by using the generated
micronanobubbles, so that oil and fat contents causing the clogging of
the submerged membrane can effectively be washed away.

[0031]In one embodiment of the invention, the aeration tank has an air
diffusion pipe for discharging air to the submerged membrane to clean the
submerged membrane, and

[0032]the submerged membrane is cleaned with mixed bubbles composed of
micronanobubbles generated by the micronanobubble cleaning section and
air discharged from the air diffusion pipe.

[0033]According to the wastewater treatment equipment in this embodiment,
the submerged membrane in the aeration tank can be cleaned by two kinds
of mixed bubbles: micronanobubbles generated by the micronanobubble
cleaning section and large air bubbles discharged from the air diffusion
pipe. Therefore, the synergistic effects of these two kinds of bubbles
can be obtained by exerting the respective capabilities of these two
kinds of bubbles. Thereby more reliable cleaning of the submerged
membrane can be achieved. More particularly, air bubbles from the air
diffusion pipe move toward the submerged membrane in such a way that
micronanobubbles excellent in cleaning effect can be guided to the
submerged membrane.

[0034]In one embodiment of the invention, the air diffusion pipe is placed
below the submerged membrane while the micronanobubble cleaning section
is placed between the submerged membrane and the air diffusion pipe, and

[0035]there are provided: a first guide mounted on the air diffusion pipe
for guiding air discharged from the air diffusion pipe to the
micronanobubble cleaning section; and

[0036]a second guide mounted on the submerged membrane for guiding
micronanobubbles generated by the micronanobubble cleaning section and
air discharged from the air diffusion pipe to the submerged membrane.

[0037]According to the effluent treatment device in this embodiment, the
first and second guides can laconically bring the micro nano bubbles,
which are generated in the micro nano bubble cleaning section, and air
bubbles, which are generated by the air diffusion pipe, into contact with
the submerged membrane. This allows more reliable cleaning of the
submerged membrane.

[0038]In one embodiment of the invention, the aeration tank has a
plurality of submerged membranes placed vertically in two or more rows.

[0039]According to the wastewater treatment equipment in this embodiment,
a plurality of the submerged membranes are placed in two or more rows in
vertical direction in the aeration tank. This makes it possible to reduce
the installation floor space for the aeration tank, thereby making it
possible to provide space saving equipment.

[0040]In one embodiment of the invention, the photocatalyst tank has

[0041]an ultraviolet irradiation section; and

[0042]a photocatalyst plate which comes into contact with the treatment
water and which includes a sputtered thin film irradiated with
ultraviolet light from the ultraviolet irradiation section.

[0043]According to the wastewater treatment equipment in this embodiment,
the ultraviolet irradiation section applies ultraviolet light to the
photocatalyst plate so as to be able to increase the photocalytic effect
of the photocatalyst plate. Moreover, the sputtered thin film included in
the photocatalyst plate can be made into a close-grained thin film with
high hardness as a photocatalyst. Therefore, the sputtered thin film is
free from wear and detachment from the photocatalyst plate even when it
is impacted by intense water flow. The ultraviolet irradiation section is
preferably placed in a location away from the treatment water. The
ultraviolet irradiation section may be constituted of a mercury lamp and
the like.

[0044]In one embodiment of the invention, the photocatalyst tank has

[0045]a light emitting diode lamp; and

[0046]a photocatalyst plate which comes into contact with the treatment
water and which includes a sputtered thin film irradiated with light from
the light emitting diode lamp.

[0047]According to the wastewater treatment equipment in this embodiment,
applying light beams from the light emitting diode lamp, which is in
noncontact with the treatment water, to the photocatalyst plate can
enhance the photocalytic effect of the photocatalyst plate. Moreover, the
light emitting diode lamp does not contain mercury unlike ultraviolet
lamps, and therefore the light emitting diode lamp is environmentally
safe. The light emitting diode lamp is preferably placed in a location
away from the treatment water.

[0048]In one embodiment of the invention, the photocatalyst plate includes
the sputtered thin film and a substrate which is made of either glass or
quart.

[0049]According to the wastewater treatment equipment in this embodiment,
the photocatalyst plate is made of glass or quart, and therefore is
inexpensive and easy to manufacture.

[0050]In one embodiment of the invention, the photocatalyst tank has a
micronanobubble generator.

[0051]According to this embodiment, the photocatalyst tank can increase
the efficiency of contact between treatment water and the photocatalyst
plate by generating micronanobubbles with use of the micronanobubble
generator. Furthermore, it is possible to oxidize residual organic matter
in treatment water in a short time by using two oxidations, oxidation
with use of micronanobubbles and oxidation with photocatalyst.

[0052]In one embodiment of the invention, the aeration tank receives
treatment water subjected to biological treatment or sludge generated
after biological treatment.

[0053]According to the wastewater treatment equipment in this embodiment,
the aeration tank receives treatment water subjected to biological
treatment or sludge generated after the biological treatment. This makes
it possible to reinforce the activity of microorganisms in the aeration
tank. More particularly, culturing high concentrations of microorganisms
requires minerals in the treatment water subjected to biological
treatment or in the sludge generated after the biological treatment.
Shortage of the minerals causes poor activity of microorganisms.
Moreover, treatment water rich in electrolyte can be obtained by
introducing the treatment water subjected to biological treatment or the
sludge resulting from the biological treatment, which are sources of
electrolyte ions, into the aeration tank.

[0054]In one embodiment of the invention, the photocatalyst tank is
structured to have a transparent outer wall, and the ultraviolet
irradiation section is placed around the transparent outer wall.

[0055]According to the wastewater treatment equipment in this embodiment,
the photocatalyst tank has a transparent outer wall, so that outside
light incoming through the transparent outer wall can increase the
photocalytic action of the photocatalyst plate and thereby enhance the
treatment efficiency of treatment water through the photocalytic action.
Making the entire surfaces of the outer wail transparent allows the light
incoming from upper, lower and side surfaces, so that the photocalytic
action is further enhanced.

Effect of the Invention

[0056]According to the wastewater treatment method in this invention, the
treatment water is subjected to the micronanobubble treatment step, in
which the organic matter in the wastewater containing organic matter is
pretreated with micronanobubbles, and then the treatment water is
subjected to microbial treatment in the microbial treatment step.
Therefore, the pretreatment with use of the micronanobubbles increases
the activity of microorganisms, and thereby it is possible to reduce
organic matter load and downsize the device for microbial treatment.
Further, the treatment water is subjected to photocalytic treatment after
the microbial treatment in the microbial treatment step, and thereby it
becomes possible to treat a minute amount of residual organic matter.
This makes it possible to perform an advanced treatment beyond the limit
of the treatment by the microbial treatment.

[0057]Therefore, according to the wastewater treatment method in the
present invention, it becomes possible to enhance treatment efficiency of
wastewater containing organic matter and to achieve reduction in scale of
the wastewater treatment equipment as well as reduction in running cost.

BRIEF DESCRIPTION OF THE DRAWINGS

[0058]FIG. 1 shows a schematic view of an effluent treatment device in a
first embodiment of the present invention;

[0059]FIG. 2 shows a schematic view of an effluent treatment device in a
second embodiment of the present invention;

[0060]FIG. 3 shows a schematic view of an effluent treatment device in a
third embodiment of the present invention;

[0061]FIG. 4 shows a schematic view of an effluent treatment device in a
fourth embodiment of the present invention;

[0062]FIG. 5A shows a time chart in the case where total organic carbon
concentration of wastewater containing organic matter in the first to
fourth embodiments is 800 ppm; and

[0063]FIG. 5B shows a time chart in the case where total organic carbon
concentration of wastewater containing organic matter in the first to
fourth embodiments is 1600 ppm.

[0090]Hereinbelow, the present invention will be described in detail in
conjunction with embodiments with reference to the drawings.

First Embodiment

[0091]FIG. 1 shows a schematic view of wastewater treatment equipment in a
first embodiment of the present invention. In the first embodiment, the
wastewater treatment equipment has an adjustment tank 1, a
micronanobubble reaction vessel 3, an aeration tank 7 and a photocatalyst
tank 22.

[0092]Wastewater containing organic matter is introduced into the
adjustment tank 1, where the quantity and the quality of the wastewater
containing organic matter are adjusted. The wastewater introduced into
the adjustment tank 1 may include various kinds of wastewater containing
organic matter such as wastewater from food factories and organic alkali
wastewater from semiconductor factories, for example. Domestic wastewater
is also included in the wastewater containing organic matter since
domestic wastewater contains organic matter. The wastewater containing
organic matter is adjusted as to its quantity and quality in the
adjustment tank 1, and is then introduced into the micronanobubble
reaction vessel 3 by an adjustment tank pump 2 as treatment water.

[0093]A micronanobubble generator 4 is placed inside of the
micronanobubble reaction vessel 3. An air suction pipe 5 and a water pipe
29 are connected to the micronanobubble generator 4. Through the air
suction pipe 5, air is introduced into the micronanobubble generator 4.
Through the water pipe 29, treatment water is fed into the
micronanobubble generator 4, where the treatment water is conveyed by a
water pump 19 from a submerged membrane 17 placed inside the aeration
tank 7. In this way, the micronanobubble generator 4 generates
micronanobubbles.

[0094]The water pipe 29 and the water pump 19 constitute a water
conveyance section. The micronanobubble generator 4 is not limited by
manufacturers, but any micronanobubble generator available in the market
can be used therefor. For a specific example, it is possible to adopt a
micronanobubble generator made by Nanoplanet Research Institute
Corporation. It is also possible as other available products to adopt
micronanobubble water generating apparatuses made by Aura Tec
Corporation, Shigenkaihatsu Corporation, or made by Seika Corporation.

[0095]In the micronanobubble reaction vessel 3, the organic matter
contained in the wastewater is partially oxidized by micronanobubbles.
Then, the treatment water partially oxidized is introduced into the
aeration tank 7.

[0096]The aeration tank 7 is equipped with a circulating pump 6. The
circulating pump 6 introduces sludge into the micronanobubble reaction
vessel 3 through a circulating pipe L1, wherein the sludge includes the
treatment water in the aeration tank 7. The sludge in the micronanobubble
reaction vessel 3 is treated with use of micronanobubbles generated by
the micronanobubble generator 4, and then returned to the aeration tank
7.

[0097]In other words, the sludge including the treatment water is
circulated between the aeration tank 7 and the micronanobubble reaction
vessel 3 by the circulating pump 6. During circulation of the treatment
water with use of the circulating pump 6, oxygen is supplied to the
treatment water to oxidize the treatment water by micronanobubbles.
Particularly, it has been found out that nanobubbles stay in water for
ever to increase dissolved oxygen concentration.

[0098]There are three kinds of babble as follows, and description is given
thereof.

[0099](i) general bubbles rise in water to end up bursting on the surface
and disappear.

[0100](ii) micro bubbles, which are fine bubbles with a diameter of 50
microns (μm) or less, shrink in water and end up disappearing (i.e.
completely dissolving).

[0101](iii) nano bubbles are smaller than micro bubbles and have a
diameter of several hundred nm or less (e.g., diameter of 100 to 200 nm),
are said to be able to keep on existing in water permanently.

[0102]Thus, the micronanobubbles are bubbles which are formed by mixture
of the microbubbles and the nanobubbles.

[0103]The water is circulated by the circulating pump 6 from the submerged
membrane 17 in the aeration tank 7 through the water pipe 29 to the
micronanobubble reaction vessel 3, so that the circulated water is
introduced into the micronanobubble generator 4 in the micronanobubble
reaction vessel 3. Consequently, the circulated water is supplied with
oxygen by using micronanobubbles. Nanobubbles in the micronanobubble
remain in treatment water inside the aeration tank 7 for a long period of
time, so that the dissolved oxygen in the aeration tank 7 is maintained
for a long period of time.

[0104]In conventional aeration tanks where oxygen supply by
micronanobubbles is not available, an aerating blower operates for 24
hours. In the present embodiment, on the other hand, the aeration tank 7
is intermittently aerated by the air bubbles discharged from a diffusion
pipe 8, to which the air is supplied through an air pipe 10 by a blower 9
which is intermittently operated. The intermittent operation by the
intermittent operation blower 9 can save energy in comparison with
continuous operation.

[0105]As shown in FIG. 1, the aeration tank 7 is equipped with three water
pumps 19, 20, 21 each connected to the submerged membrane 17.

[0106]As described before, the water pump 19 conveys treatment water from
the submerged membrane 17 to the micronanobubble reaction vessel 3 The
water pump 20 conveys treatment water from the submerged membrane 17 to a
micronanobubble generator 15 for cleaning the submerged membrane 17
through a water pipe 13. An air suction pipe 14 is connected to the
micronanobubble generator 15, so that air is introduced into the
micronanobubble generator 15 through the air suction pipe 14.

[0107]The water pump 21 conveys treatment water from the submerged
membrane 17 to a micronanobubble generator 25 through a water pipe 27,
where micronanobubble generator 25 is placed in the photocatalyst tank 22
provided downstream of the aeration tank 7. An air suction pipe 26 is
connected to the micronanobubble generator 25, so that air is introduced
from the air suction pipe 26 into the micronanobubble generator 25.

[0108]The submerged membrane 17 is also equipped with a submerged membrane
cover 16 as a second guide. When the air is discharged and ascends from
an air diffusion pipe 11, which is placed below the micronanobubble
generator 15, the submerged membrane cover 16 plays a role of guiding
super fine micronanobubbles, together with the air discharged from the
air diffusion pipe 11, to the submerged membrane 17 so as to effectively
contact with the submerged membrane 17.

[0109]The air diffusion pipe 11 connected to a blower 28 is also equipped
with an air diffusion pipe cover 12 as a first guide. The air diffusion
pipe cover 12 plays a role of efficiently guiding the air discharged from
the air diffusion pipe 11 to the micronanobubble generator 15. The blower
28, which supplies air to the air diffusion pipe 11, continuously
operates for 24 hours. The reason of the continuous operation is that air
cleaning of the submerged membrane 17 needs 24 hours' operation.

[0110]The operating time of the micronanobubble generator 15 may be
determined in association with the clogging state of the submerged
membrane 17. More specifically, in the case where treatment water
contains a large amount of oil and fat contents, the operating time of
the micronanobubble generator 15 generally becomes relatively long. The
air supplied from the blower 28 to the air diffusion pipe 11 is
discharged from the air diffusion pipe 11 and cleans the surface of the
submerged membrane 17. Mixed bubbles, which are composed of
micronanobubbles and the air discharged from the air diffusion pipe 11,
have higher effect of cleaning the submerged membrane 17.

[0111]Treatment water, which is subjected to biological treatment or
sludge generated by biological treatment, is introduced into the aeration
tank 7 through a pipe L2. The biologically treatment water or the
biologically treated sludge includes microelements such as phosphorus,
potassium, calcium and magnesium. The microelements promote s activity of
all the microorganisms in the aeration tank 7. Unless the microelements
are sufficiently contained in the water, the treatment unstable because
microorganisms stay inactive in high-concentration microbial treatment,
in particular, with use of the submerged membrane 17 within the aeration
tank 7. The aeration tank 7 is operated with a microbial concentration of
10,000 ppm or higher in terms of MLSS (Mixed Liquor Suspended Solid)
concentration. The treatment water comes out of the submerged membrane
17, and is introduced into the photocatalyst tank 22 through a gravity
pipe 18-A. The treatment water is introduced through the gravity pipe
18-A by using water head difference.

[0112]The photocatalyst tank 22 is equipped with an ultraviolet lamp 23 as
an ultraviolet irradiation section, which lamp is placed on the uppermost
section of the tank in such a way that treatment water does not reach the
ultraviolet lamp 23. Inside the photocatalyst tank 22, the
micronanobubble generator 25 is also placed. A photocatalyst plate 24 is
placed between the ultraviolet lamp 23 and the micronanobubble generator
25. The photocatalyst plate 24 contacts with treatment water, whereas the
ultraviolet lamp 23 does not contact with the treatment water.

[0113]In the photocatalyst tank 22, the treatment water is mixed and
agitated with the photocatalyst of the photocatalyst plate 24 by using
the micronanobubbles generated by the micronanobubble generator 25, and
also the treatment water is oxidized by the micronanobubbles. The
photocatalyst plate 24 has specifically been manufactured by forming a
sputtered thin film on a glass plate by using the sputtering method.
Generally, the ultraviolet lamp 23 contains harmful mercury. Therefore,
an environmentally-safe light emitting diode lamp may be employed in
place of the ultraviolet lamp 23. The water fed to the micronanobubble
generator 25 is the treatment water supplied through the water pipe 27 by
the water pump 21 which is connected to the submerged membrane 17.

[0114]Then, treated water is obtained from an outlet of the photocatalyst
tank 22. According to the wastewater treatment equipment in the first
embodiment, wastewater containing organic matter is treated with
micronanobubbles in the micronanobubble reaction vessel 3, and then
introduced into the aeration tank 7 having the submerged membrane 17.
This allows the treatment to be carried out in the sate that the activity
of microorganisms is enhanced by micronanobubbles. At the same time, the
wastewater containing organic matter is treated with micronanobubbles in
the micronanobubble reaction vessel 3 prior to microbial treatment in the
aeration tank 7. Therefore, it becomes possible to achieve
miniaturization of the aeration tank 7, reduction in scale of the whole
equipment and reduction in initial cost. Moreover, the organic matter
contained in wastewater is oxidized with micronanobubbles. Thereby, the
organic matter load is reduced. Thereafter, the treatment water is
introduced into the aeration tank 7 where microorganisms are present in
high concentration due to submerged membrane 17. Thereby, treatment of
the organic matter is effectively accomplished. In photocatalyst tank 22
provided downstream of the aeration tank 7, it is possible to perform
high-level oxidation treatment of organic matter by oxidation with use of
the photocatalyst. This oxidation treatment can treat such a minute
amount of organic matter as the microbial treatment alone cannot treat.

[0115]According to the present embodiment, it is possible to enhance the
efficiency of contact between the treatment water and the photocatalyst
plate 24 in the photocatalyst tank 22, by using micronanobubbles
generated by the micronanobubble generator 25. Furthermore, it is
possible to oxidize residual organic matter in treatment water in a short
period of time by both the oxidation with micronanobubbles and the
oxidation with photocatalyst.

[0116]According to the first embodiment, therefore, the treatment
efficiency of wastewater containing organic matter is not only enhanced,
but also reduction in scale of the wastewater treatment equipment and
reduction in running cost can be achieved.

[0117]In the first embodiment, the water pump 19 and the water pipe 29,
which constitute a water conveyance section, convey the treatment water
from the aeration tank 7 through the submerged membrane 17 to the
micronanobubble generator 4 provided in the micronanobubble reaction
vessel 3. In other words, the treatment water, which contains electrolyte
and is treated by the submerged membrane, is conveyed from the aeration
tank 7 to the micronanobubble generator 4. The aeration tank 7 is a
high-concentration biological treatment device utilizing the submerged
membrane 17. Thus, the micronanobubble generator 4 can stably supply
extremely fine air bubbles in the micronanobubble reaction vessel 3.

Second Embodiment

[0118]FIG. 2 shows wastewater treatment equipment in a second embodiment
of the present invention. The second is embodiment is different from the
first embodiment only in the point that an aeration tank 7N is equipped
with other submerged membranes 117 placed above the submerged membrane
17. Consequently, in the second embodiment, the component parts identical
to those in the first embodiment are designated by identical reference
numerals, and description will be omitted except the component parts
different from the first embodiment.

[0119]In the second embodiment, as shown in FIG. 2, the submerged membrane
117 is placed above the submerged membrane 17 in such a way that two
submerged membranes 17 and 117 are placed three-dimensionally. This
allows effectively three-dimensional utilization of the micronanobubbles
and cleaning air when they ascend along the submerged membranes 17 and
117, without increasing the installation floor space for the aeration
tank 7.

Third Embodiment

[0120]FIG. 3 shows wastewater treatment equipment in a third embodiment of
the present invention. The third embodiment is different from the
aforementioned first embodiment only in the point that an aeration tank
7V is filled with a polyvinylidene chloride filling 30. Consequently, in
the third embodiment, the component parts identical to those in the first
embodiment are designated by identical reference numerals, and
description will be omitted except the component parts different from the
first embodiment.

[0121]In the third embodiment, since the aeration tank 7V is filled with
polyvinylidene chloride filling 30, the whole aeration tank 7V has higher
microbial concentration on an average than the aeration tank without the
filling 30. In addition, microorganisms attach to the polyvinylidene
chloride filling 30 and proliferate thereon. Therefore, the
microorganisms are more stabilized, and also the capability to treat
organic matter in the wastewater containing organic matter is enhanced,
compared with the aeration tank without the filling.

[0122]It is preferable that the polyvinylidene chloride filling 30 is
placed entirely in the tank 7V. In such a case, the concentration of
overall microorganism becomes high in the aeration tank 7V.

[0123]In the third embodiment, microorganisms proliferate on the
polyvinylidene chloride filling 30 as time proceeds starting from an
initial run. The microorganism concentration becomes 30,000 ppm or more
on the surface of the polyvinylidene chloride filling 30, which
contributes to increase in treatment efficiency of organic matter. The
polyvinylidene chloride filling 30 is made of vinylidene chloride.
Vinylidene chloride is solid and resistant to chemical substances, so
that it can be used semipermanently. For the polyvinylidene chloride
filling 30, the products are available under the product name such as
Biocode, Ling-Lace, BioMultiLeaf and BioModule. Any of them may be
selected depending on the properties of wastewater. The third embodiment
may be combined with the second embodiment.

Fourth Embodiment

[0124]FIG. 4 shows wastewater treatment equipment in a fourth embodiment
of the present invention. The fourth embodiment is different from the
aforementioned first embodiment only in the point that a separation plate
31 extending in a vertical direction is placed in the vicinity of
approximately the center of an aeration tank 7Z. Consequently, in the
fourth embodiment, the component parts identical to those in the first
embodiment are designated by identical reference numerals, and
description will be omitted except the component parts different from the
first embodiment.

[0125]In the fourth embodiment, the air supplied by the blower 28 and
discharged from the air diffusion pipe 11 generates an ascending water
flow 32A in the aeration tank 7Z. The ascending water flow 32A moves
beyond the separation plate 31, which is positioned approximately in the
center, to the opposite side of the air diffusion pipe 11, where it
becomes a descending water flow 32B. This provides sufficient agitation
in the aeration tank 7Z, so that microbial decomposition of the organic
matter in treatment water is promoted. The fourth embodiment may be
combined with the aforementioned second and third embodiments.

Experimental Example

[0126]There was experimental equipment having a configuration identical to
that of the wastewater treatment equipment in the first embodiment shown
in FIG. 1. The capacities of the adjustment tank 1, the micronanobubble
reaction vessel 3, and the aeration tank 7 were 50, 20 and 200 liters,
respectively in the experimental equipment. Microorganisms were cultured
for two months to have a microbial concentration of 14,000 ppm in the
experimental equipment. Wastewater containing organic matter discharged
from a factory is used for this experiment, wherein the wastewater has an
organic matter concentration of 860 ppm as measured in TOC (Total Organic
Carbon). This wastewater was continuously introduced into the adjustment
tank 1. Thereafter, one month elapsed and the water quality was
stabilized. Then, TOC of wastewater obtained from the outlet port of the
gravity pipe 18-B was measured, and the result of measurement was 12 ppm.

[0127]FIG. 5A shows an example of a time chart in the first to fourth
embodiments in the case where the wastewater containing organic matter
has TOC of 800 ppm. FIG. 5B shows an example of a time chart in the first
to fourth embodiments in the case where the wastewater containing organic
matter has TOC of 1,600 ppm. Moreover, in the first to fourth
embodiments, making the outer wall of the photocatalyst tank 22
transparent allows outside light incoming through the transparent outer
wall to increase the photocalytic action of the photocatalyst plate 24.
This makes it possible to enhance the treatment efficiency of treatment
water through the photocalytic action. Particularly, making the entire
surfaces of the outer wall transparent allows the light incoming from
upper, lower and side surfaces to further enhance the photocalytic
action.